U.S. patent application number 09/996911 was filed with the patent office on 2002-06-06 for electrophoretic display device.
Invention is credited to Matsuda, Yojiro, Uno, Yoshinori.
Application Number | 20020067333 09/996911 |
Document ID | / |
Family ID | 26605093 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067333 |
Kind Code |
A1 |
Uno, Yoshinori ; et
al. |
June 6, 2002 |
Electrophoretic display device
Abstract
In an electrophoretic display device, comprising: a pair of
substrates opposing to each other with a gap therebetween, a spacer
keeping the gap between the substrates to a predetermined extent,
first electrodes and second electrodes disposed on either one of
the substrates, an insulating liquid filling the gap between the
substrates, and a plurality of charged electrophoretic particles
carried in the insulating liquid, the plurality of charged
electrophoretic particles being capable to move in response to a
voltage applied between the first aid second electrodes; the
display region of the device is divided into pixels each having at
least a pair of the first and the second electrodes, at least one
of the first electrodes in a pixel, is disposed along and adjacent
to the whole or a part of the boundary of the pixel, and the one of
the first electrodes in a pixel and said one of the first
electrodes in another pixel which are disposed adjacently to each
other vita the pixel boundary have the same potential.
Inventors: |
Uno, Yoshinori; (Kanagawa,
JP) ; Matsuda, Yojiro; (Kanagawa, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26605093 |
Appl. No.: |
09/996911 |
Filed: |
November 30, 2001 |
Current U.S.
Class: |
345/107 |
Current CPC
Class: |
G02F 1/134363 20130101;
G09G 2320/0209 20130101; G02F 1/167 20130101; G09G 3/3446
20130101 |
Class at
Publication: |
345/107 |
International
Class: |
G09G 003/34 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2000 |
JP |
367328/2000 |
Jun 26, 2001 |
JP |
193730/2001 |
Claims
What is claimed is:
1. An electrophoretic display device, comprising: a pair of
substrates opposing to each other with a gap therebetween, a spacer
keeping the gap between the substrates to a predetermined extent,
first electrodes and second electrodes disposed on either one of
the substrates, an insulating liquid filling the gap between the
substrates, and a plurality of charged electrophoretic particles
carried in the insulating liquid, the plurality of charged
electrophoretic particles being capable to move in response to a
voltage applied between the first and second electrodes; wherein,
the display region of the device is divided into pixels each having
at least a pair of the first and the second electrodes, at least
one of the first electrodes in a pixel is disposed along and
adjacent to the whole or a part of the boundary of the pixel, and
said one of the first electrodes in a pixel and said one of the
first electrodes in another pixel which are disposed adjacently to
each other via the pixel boundary have the same potential.
2. The electrophoretic display device according to claim 1, wherein
the first electrodes are disposed in parallel to at least part of
the pixel boundary and in a constant width.
3. The electrophoretic display device according to claim 1, wherein
the first electrode potential is fixed and the second electrode
potential is applied independently for each pixel, to cause the
charged electrophoretic particles to move to perform display.
4. The electrophoretic display device according to claim 1, wherein
the first electrodes are connected in common in the row direction
and second electrodes are connected in common in the column
direction to set a voltage for each pixel through the first and the
second electrodes, to cause the charged electrophoretic particles
to move to perform display.
5. The electrophoretic display device according to claim 1, wherein
each pixel is provided therein with at least one second electrode
and first electrodes so disposed as to surround the. second
electrode.
6. The electrophoretic display device according to claim 1, wherein
the first electrode of one pixel and the first electrode of the
other pixel which are disposed adjacently to each other are
integrally formed.
7. The electrophoretic display device according to claim 1, wherein
the first electrode is provided in plurality in each pixel, and a
plurality of first electrodes are electrically connected to each
other.
8. The electrophoretic display device according to claim 7, wherein
at least three first electrodes and at least two second electrodes
are alternately disposed in each pixel.
9. The electrophoretic display device according to claim 1, wherein
the first electrode and the second electrode are formed on
different planes so as to have different heights from the
substrate.
10. The electrophoretic display device according to claim 1,
wherein an auxiliary electrode connected electrically to the first
electrode is disposed on an area including the position where the
absolute value of the horizontal component of electric field
vectors produced above the first electrode assumes the minimum
value when a drive voltage of an equal potential, different from
the potential of the first electrode is applied to the respective
second electrodes of adjoining pixels.
11. The electrophoretic display device according to claim 10,
wherein the auxiliary electrode is disposed on the first electrode
via an insulating layer.
12. The electrophoretic display device according to claim 10,
wherein the auxiliary electrode is a protrusion structure provided
on the first electrode.
13. The electrophoretic display device according to claim 1,
wherein an insulating layer is so disposed as to cover the first
electrode and the second electrode.
14. The electrophoretic display device according to claim 1,
wherein a partition wall which restricts the charged
electrophoretic particles from moving unwantedly is provided at the
pixel boundary.
15. The electrophoretic display device according to claim 1,
wherein a microcapsule which encapsulates the insulating liquid and
the charged electrophoretic particles within a transparent film is
disposed between the pair of substrates.
16. The electrophoretic display device according to claim 1,
wherein wirings or switching elements, or the both thereof,
connected to the first electrode and second electrode are shielded
with any one or both electrode face(s) of the first electrode and
second electrode, and are disposed at a position not having any
electrical influence on the region in which the charged
electrophoretic particles are present.
17. The electrophoretic display device according to claim 1,
wherein the first electrode and the second electrode are formed on
vertically shifted different planes, and are so formed that the
edge portions of the respective electrodes overlap each other at
the boundary between the first electrode and the second electrode.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an electrophoretic display device,
which performs display by moving charged electrophoretic
particles.
[0003] 2. Related Background Art
[0004] In recent years, with advancement of information machinery,
the quantity of data of various information becomes larger and
larger, and the information is outputted in various forms.
[0005] Methods of outputting information are commonly roughly
grouped into.
[0006] (1) a method of performing display by means of display
devices such as a CRT (cathode ray tube) and a liquid crystal
display panel; and
[0007] (2) a method of performing display by taking hard copies on
paper using a printer or the like.
[0008] Among the display devices in the method (1), the liquid
crystal display panel, is being spotlighted in recent years because
of its characteristic features that it requires only a small power
consumption and also can be thin-shaped. It, however, also has
problems that characters displayed on its screen may be viewed with
difficulty depending on angles at which you look at the screen or
under the influence of reflected light and that the burden on
eyesight which is caused by flickering, low luminance and so forth
of its light source has not well been solved.
[0009] On the other hand, CRT is superior to the liquid crystal
display panel in regard to contrast and luminance. However, in
respect of the occurrence of flickering, it can not be said to have
a sufficient display quality level compared with the hard-copy
display in the method (2). It also has a problem that the display
unit is so large and heavy as to have a very low portability.
[0010] The hard copies in the method (2) have at first been
considered to become unnecessary with spread of display devices,
but in fact they are frequently utilized. As reasons therefor, the
following can be given. First, it can be pointed out that, in the
case of display devices, not only the burden on eyesight has not
well been solved as stated above, but also they have a low
resolution (120 dpi at maximum), to which the hard copies have a
superiority (300 dpi or higher). Second, it can be pointed out
that, only the information displayed on the screen can be viewed in
the case of display devices, whereas, in the case of the hard
copies, a plurality of copies can be arranged to compare each other
and can be rearranged without any complicate operation or can be
checked in order. Third, it can be pointed out that the hard copies
do not require any energy (power) for retaining the display, and
are portable as long as the volume (i.e., the number of hard
copies) is not so extremely large, making it possible to check the
information anytime and anywhere.
[0011] As long as any motion picture display or frequent rewriting
is not required, the hard copies still have a great advantage
compared with display devices as stated above, but on the other
hand have a problem that paper is consumed in a large quantity.
[0012] Accordingly, in recent years, development is energetically
put forward on a rewritable recording medium (a medium on which
sharp images can repeatedly be recorded and erased and which does
riot require any energy for retaining the display). The third way
of display which has succeeded the features of the hard copies and
in which the display is rewritable. is herein called "paper like
display".
[0013] Requirements for the paper like display are that the display
is rewritable, that any energy is not required or sufficiently a
low energy is enough to retain the display (memory performance),
that the display has a good portability, that the display has a
good quality level, and so forth. An example which, at present, can
be regarded as a paper like display is the reversible display
medium made from an organic low molecular and high molecular resin
matrix system, which which is recorded and erased with a thermal
printer head (e.g., Japanese Patent Applications Laid-Open No.
55-154198 and No. 57-82086). Such a medium is some utilized as a
display part of a prepaid card, but has problems such that the
contrast is not so high and the writing and erasing can only be
repeated relatively as small as 150 to 500 times.
[0014] As another way of display which is expected to be utilized
for the paper-like display, an electrophoretic display device
invented by Harold. D. Lees et. al. is known (U.S. Pat. No.
3,612,758). Besides, Japanese Patent Application Laid-Open No.
9-185087 discloses an electrophoretic display device,
[0015] The electrophoretic display device of this type has a pair
of substrates disposed leaving a gap between them, an insulating
liquid with which the gap between the substrates is filled, a large
number of colored charged electrophoretic particles dispersed in
the insulating liquid, and a pair of electrodes so disposed as to
sandwich the insulating liquid between them. In such a device, with
changes of the voltage polarity applied to the electrodes, the
colored charged electrophoretic particles are attracted to the
electrode on this side (viewer's side) or attracted to the
electrode on the other side. When the colored charged
electrophoretic particles are kept attracted to the electrode on
this side, the color of the particles is perceived. When the
colored charged electrophoretic particles are kept attracted to the
electrode on the other side, the color of the insulating liquid is
perceived. Thus, various images can be displayed by controlling the
polarity of applied voltage for each pixel.
[0016] In such an electrophoretic display device, however, the
colored charged electrophoretic particles are so made as to be
freely movable from pixels to pixels, and hence there has been a
problem that they can not be distributed in a uniform density,
resulting in a poor display quality level.
[0017] As a device that can solve such a problem, Japanese Patent
Applications Laid-Open No. 59-171930 and No. 01-196094 disclose a
display device having a partition wall so disposed as to separate
pixels from each other to block any unauthorized movement of
colored charged electrophoretic particles.
[0018] Now, in the case of the electrophoretic display device of
the type described above, a color-developing material
(color-developing material such as a dye and ions) must be mixed in
the insulating liquid for the purpose of coloring. However, this
color-developing material may cause the delivering and receiving of
electric charges with the electrophoretic particles, so that it may
adversely affect the electrophoretic motion of the electrophoretic
particles to lower the performance, lifetime and stability required
as display devices.
[0019] As a device that can solve such a problem, Japanese Patent
Applications Laid-Open No. 49-024695 and No. 11-202804 disclose an
electrophoretic display device of a type shown in FIG. 13
(hereinafter "horizontal movement type electrophoretic display
device"). Such a horizontal movement type electrophoretic display
device has a pair of substrates 1a and 1b disposed leaving a gap
between them, an insulating liquid 4 with which the gap between the
substrates 1a and 1b is filled, a large number of colored charged
electrophoretic particles 5 dispersed in the insulating liquid, and
a pair of electrodes 66 and 67 disposed in each pixel A. The pair
of electrodes 66 and 67, however, are not so disposed as to
sandwich the insulating liquid 4 between them like the type
described previously, but are so disposed as to be arranged on one
substrate 1a. In the case of such a horizontal. movement type
electrophoretic display device, the insulating liquid 4 may be
transparent and any color developing material need not be mixed.
Hence, the problem as stated above can be avoided. Also, in this
device, one electrode 66 (here a first electrode 66) is covered
with a colored layer 8a having the same color (e.g., black color)
as the charged electrophoretic particles 5, and the other electrode
67 (here a second electrode 67) is covered with a colored layer 8b
having a different color (e.g., white color). The colored charged
electrophoretic particles 5 move horizontally (in the direction
parallel to the substrate) in accordance with the polarity of the
voltage applied to the electrodes 66 and 67, and are attracted to
the first electrode 66 or second electrode 67. When the colored
charged electrophoretic particles 5 are kept attracted to the first
electrode 66, the color of the particles is readily perceived. When
the colored charged electrophoretic particles 5 are kept attracted
to the second electrode 67, the whole pixel is perceived in the
same color as the charged electrophoretic particles 5. Thus,
various images can be displayed by controlling the polarity of
applied voltage for each pixel.
[0020] Now, in the horizontal movement type electrophoretic display
device as described above, colored charged electrophoretic
particles 5A.sub.1 disposed in a certain pixel A.sub.1 are desired
to be controlled only by the voltage applied to electrodes
66A.sub.1 and 67A.sub.1 of the pixel A.sub.1. However, the colored
charged electrophoretic particles 5A.sub.1 may move irregularly
under the influence of an electric field of an adjoining pixel
A.sub.2 (i.e., the voltage applied to electrodes 66A.sub.2 and
67A.sub.2 of the pixel A.sub.2 ) to cause a disorder of display and
a decrease in contrast.
[0021] In the case of a method of performing display by forming
electric field distribution in the horizontal direction (i.e., in
the above horizontal movement type electrophoretic display device),
like electrophoretic display intended in the present invention,
various wirings and switching elements connected to electrodes and
switching elements may partly stand uncovered in regions where any
electrodes (display electrodes) are formed (e.g., the boundary
region between the first electrode and the second electrode and the
boundary region between pixels), and there has also been a serious
problem that any leaked electric field the wirings and switching
elements may cause makes the electrophoretic particles move in the
vicinity of the wiring of display pixels, resulting in a poor
display quality.
SUMMARY OF THE INVENTION
[0022] Accordingly, an object of the present invention is to
provide an electrophoretic display device which prevents any
deterioration of display quality stated above.
[0023] The present invention was made taking account of the above
circumstances, and provides an electrophoretic display device,
comprising:
[0024] a pair of substrates opposing to each other with a gap
therebetween,
[0025] a spacer keeping the gap between the substrates to a
predetermined extent,
[0026] first electrodes and second electrodes disposed on either
one of the substrates,
[0027] an insulating liquid filling the gap between the substrates,
and
[0028] a plurality of charged electrophoretic particles carried in
the insulating liquid,
[0029] the plurality of charged electrophoretic particles being
capable to move in response to a voltage applied between the first
and second electrodes, wherein,
[0030] the display region of the device is divided into pixels each
having at least a pair of the first and the second electrodes, at
least one of the first electrodes in a pixel is disposed along and
adjacent to the whole or a part of the boundary of the pixel,
and
[0031] the one of the first electrodes in a pixel and said one of
the first electrodes in another pixel which are disposed adjacently
to each other via the pixel, boundary have the same potential.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0033] FIG. 2 is a plan view showing an example of the structure of
the electrophoretic display device according to the present
invention.
[0034] FIG. 3 is a plan view showing an example of the structure of
the electrophoretic display device according to the present
invention.
[0035] FIG. 4 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0036] FIG. 5 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0037] FIG. 6 is a plan view showing an example of the structure of
the electrophoretic display device according to the present
invention.
[0038] FIG. 7 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0039] FIG. 8 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0040] FIG. 9 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0041] FIG. 10 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0042] FIG. 11 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0043] FIG. 12 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0044] FIG. 13 is a cross sectional view showing an example of the
structure of a conventional electrophoretic display device.
[0045] FIG. 14 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0046] FIG. 15 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0047] FIG. 16 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0048] FIG. 17 is a plan view showing an example of the structure
of the electrophoretic display device according to the present
invention.
[0049] FIG. 18 is a plan view showing an example of the structure
of the electrophoretic display device according to the present
invention.
[0050] FIG. 19 is a cross sectional view showing an example of the
structure of an electrophoretic display device accord in g to the
present invention.
[0051] FIG. 20 is a cross sectional view showing an example of the
structure of an electrophoretic display device according to the
present invention.
[0052] FIG. 21 is a plan view showing an example of the structure
of the conventional electrophoretic display device.
[0053] FIG. 22 is a plan view showing an example of the structure
of the electrophoretic display device according to the present
invention.
[0054] FIGS. 23A and 23B are a cross sectional view and a plan
view, respectively, showing an example of the structure of an
electrophoretic display device according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0055] Embodiments of the present invention are described below
with reference to FIGS. 1 to 23A-23B.
[0056] The electrophoretic display device according to the present
invention has, e.g., as shown by reference symbol D.sub.1, a pair
of substrates 1a and 1b disposed leaving a stated space between
them, an insulating liquid 4 disposed at each pixel A, and a
plurality of charged electrophoretic particles dispersed in the
insulating liquid 4. Between the pair of substrates 1a and 1b, a
space support is disposed, with which the space between the
substrates is kept in a stated extent. The display device has a
plurality of pixels which divide a display region
[0057] Here, in each pixel A, a first electrode 6 and a second
electrode 7 are disposed on and in parallel to either one of the
substrates 1a and 1b (for the sake of convenience, hereinafter one
substrate on which the first electrode 6 and second electrode 7 are
disposed is called "first substrate 1a", and the other substrate,
"second substrate 1b"), the two first electrodes 6 are disposed
interposing a pixel boundary at least at a part of the pixel
boundary and adjacently to each other on both sides of the pixel
boundary. Thus, in respect of the two first electrodes 6 disposed
interposing a pixel boundary, the first electrode 6 of one pixel
and the first electrode 6 of the other pixel are disposed at a
position where they are adjacent to each other in the vicinity of
the pixel boundary, and these first electrodes 6 are so constructed
as to be electrically connected to have the same potential. Namely.
in one pixel and the other pixel which are disposed adjoiningly to
each other, the respective first electrodes 6 are disposed
adjacently to their pixel boundary (the boundary between pixels
adjoining to each other). As a result, it follows that these two
first electrode 6 are adjacently disposed interposing the pixel
boundary. Such relationship may be applied to all the pixels of the
display device, or may be applied to a part of the pixels. Also,
these two first electrodes 6 disposed adjacently to each other may
electrically be connected.
[0058] Making these electrodes have the same potential on the both
sides of the pixel boundary can prevent a strong electric field
from being produced between the pixels, and enable avoidance of the
phenomenon that the electrophoretic particles move irregularly
under the influence of an electric field of an adjoining pixel.
[0059] In the electrode structure shown in FIG. 13, when, the
electrophoretic particles (assumed to be positively charged) in the
pixel A.sub.1 are intended to be moved from the surface of the
electrode 66A.sub.1 to the surface of the electrode 67A.sub.1
without a change of display state in the pixel A.sub.2, a potential
of +50 V is applied to the electrode 66A.sub.1 and a potential of
-50 V is applied to the electrode 67A.sub.1 and both the electrodes
66A.sub.2 and 67A.sub.2 are kept at a potential of 0 V. In such a
case, the electrophoretic particles on the electrode 66A.sub.1
receives a force directed to tile electrode 67A.sub.1 at about 1/2
of the force received by electrophoretic particles on the electrode
67A.sub.1 and hence they move unwontedly in part toward the pixel
A.sub.1. Even if the electrodes in pixels whose display states are
not changed are set to have the same potential 31 50 V as the
electrode 67A.sub.1, this time a pixel on the side opposite to the
pixel A.sub.1 (not shown) is influenced. Whatever potential the
electrodes are set to have. the two electrodes interposing a pixel
boundary assume different potential when the writing in white, the
writing in black and the keeping of the display state are
performed. Hence, the unwanted movement of electrophoretic
particles necessarily takes place in that case.
[0060] On the other hand, in the case where the device has the
electrode structure as shown in FIG. 1, the writing is performed
setting the potential of the second electrode 7 at +50 V or -50 V,
and the potential of the first electrode 6 can always be kept at 0
V. Even in such a case, a force may act on the electrophoretic
particles to be kept standing in that pixel depending or, the
voltage applied to the second electrode of an adjoining pixel.
However, its magnitude is smaller than the force acting on the
electrophoretic particles i~n the pixel which performs writing.
Namely, when a potential of +50 V or -50 V is applied to the second
electrode 7 of one pixel, the intensity of an electric field
leaking to the adjoining pixel is always smaller than the electric
field intensity in that pixel. Hence, setting the movement
threshold value at a value intermediate between them, the electrode
shape and the applied voltage can be designed so that the
electrophoretic particles of the adjoining pixel, do not move.
[0061] As described above, the first electrode has the action to
make smaller the electric field leaking to the adjoining pixel than
the electric field in the pixel. For this end, it may preferably be
disposed in parallel to the pixel boundary In a width having a
stated distance to thereby make the second electrode set apart from
the pixel boundary. In such disposition, the distance from the
second electrode to an arbitrary position on the first electrode in
that pixel is smaller than the distance therefrom to an arbitrary
position on the first electrode in its adjoining pixel. Hence, the
above condition that the electric field intensity in a pixel is
greater than the intensity of an electric field leaking to the
adjoining pixel is fulfilled, This condition may not be fulfilled
at the corners of a pixel, but there is no problem in practical use
as long as this condition is fulfilled in the greater part of a
pixel.
[0062] The first electrode may be fixed to common potential in
every pixel and the second electrode may be controlled for each
pixel, thus a matrix display device can be materialized. For this
end, not shown in FIG. 1, a switching element such as TFT or MIM
may be provided for each pixel.
[0063] In general, the first electrode 6 and the second electrode 7
may be disposed at any position and may have any shape as long as
the above condition is fulfilled (i.e., the condition that two
first electrodes 6 are disposed interposing a pixel boundary at
least at part of the pixel boundary and adjacently to each other on
both sides of the pixel boundary and the electric field intensity
in a pixel is greater than the intensity of an electric field
leaking to the adjoining pixel). For example, as shown in FIG. 2,
the first electrode 6 and the second electrode 7 may be disposed
alternately in stripes. The side on which the first electrode is
not disposed adjacently to the pixel boundary and the first
electrode and second electrode are directly disposed adjacently to
each other may be so designed that the distance between pixels is
made larger or an auxiliary electrode described later may be
provided between pixels so that the electric field leaking to the
adjoining pixel can be weaker than the electric field in a pixel.
When so designed and the first electrode is disposed only in one
direction (the lateral direction in FIG. 2) of the matrix
arrangement, the potential of the first electrode must be set to
common potential in the lateral direction interposing the pixel
boundary, which potential, however, may be different in the
longitudinal direction. For example, the first electrodes may be
connected in common in the lateral direction to provide a scanning
line, and the second electrodes may be connected in common in the
longitudinal direction to provide a signal line to make up a simple
matrix drive system.
[0064] An example in which a first electrode 16 is so disposed in
the form of a frame as to surround a second electrode 17 is shown
in FIG. 3.
[0065] Here, the second electrode 17 shown in FIG. 3 is
rectangular, but by no means limited thereto of course, and it may
be circular for example. Also, the first electrode 16 shown in FIG.
3 is so disposed as to surround the four sides of the second
electrode 17, but by no means limited thereto of course, and it may
be so disposed as to surround the three sides of the second
electrode 17.
[0066] In the example shown in FIGS. 1 and 2, two first electrode 6
are disposed in one pixel A and one second electrode 7 is disposed
therein, but the example is by no means limited thereto. For
example, as shown in FIG. 4, three first electrodes 26 may be
disposed in one pixel A and two second electrodes 27 may be
disposed therein. More electrodes may be disposed. When the
electrodes 26 and 27 are disposed in a larger number, the charged
electrophoretic particles can be made to move in a short distance,
making it possible to form images at a high speed and
uniformly.
[0067] In the electrophoretic display device D.sub.1 shown in FIG.
1, the first electrodes 6 disposed in one pixel A and the first
electrodes 6 disposed in the other pixel A are also formed
separately from each other interposing each pixel boundary. These,
however, are by no means limited thereto of course, and may
integrally be formed as shown by reference numeral 26 in FIG. 4 or
by reference numeral 36 in FIG. 5. Making the first electrodes
integral in this way enables easy manufacture of display
devices.
[0068] Now, the first electrode disposed in plurality in one pixel
A may also be so constructed that, as shown by reference symbol B
in FIG. 6, as to be wire-connected to each other in the pixel and
electrically bridged to have the same potential.
[0069] In the examples shown in FIG. 1 and others, the first
electrode 6 and the second electrode 7 are formed in the same
height on the same plane. These, however, arc also by no means
limited thereto of course, and may be formed in different height on
different planes as shown by reference numerals 46 and 47 ti FIG.
7. Here, in the example shown in FIG. 7, the first electrode 46 and
the second electrode 47 are so disposed as not to overlap each
other. However, as shown in FIG. 8, the electrodes may also be so
disposed that first and second electrodes 56 and 57 overlap each
other.
[0070] In the examples shown in FIG. 1 and others, a partition wall
3 is further provided as a space support. However, a structure
having no partition wall as shown in FIG. 14 Is also feasible where
the movement threshold value of electrophoretic particles and the
electric field are properly set.
[0071] In addition, where any wirings and switching elements are
connected to the first electrode and second electrode, these
wirings and switching elements may preferably be disposed on the
first substrate side (between the first electrode and the first
substrate or between the second electrode and the first substrate)
in such a way that they are covered with the first electrode face
and/or second electrode face (any one or both electrode face(s) of
the first electrode and second electrode) as viewed from the region
in which the charged electrophoretic particles are present. With
such construction, the influence on the driving of charged
electrophoretic particles, of any leaked electric field caused by
the wirings and switching elements can be lessened or removed on
account of the effect of shielding that is attributable to the
first and second electrodes. The electrodes (display electrodes)
can be made to have the shielding effect without any additional
shielding structure provided in order to shield the electric field
having leaked from the wirings and switching elements. Thus, this
can make device construction compact and device manufacture
easier.
[0072] FIG. 22 is a plan view showing an electrophoretic display
device shown in FIG. 11. First electrodes 56 are each integrally
formed in all pixels, and are connected to a wiring 12. Also,
second electrodes 57 are each rectangular and are connected to
wirings 13. Here, the wirings 13 of the second electrodes 57 are
each disposed at a position where the second electrode is covered
with the first electrode. With such construction, any unwanted
driving of charged electrophoretic particles (namely, display
deterioration) which is caused by an electric field leaking from
the wiring 13 can be prevented on account of the shielding effect
attributable to the first electrode. In a conventional electrode
structure as disclosed in, e.g., Japanese Patent Application
Laid-Open No. 8-507154, the shielding of lead wires for feeding a
voltage to electrodes is not taken into account. However, the
double layer construction of electrodes as in the present invention
makes it possible to shield the lead wires for one electrode with
the other electrode.
[0073] As further shown in FIG. 23A, FIG. 23B being a plan view,
the first electrode 6 and the second electrode 7 may be formed in
different height on different planes and also may be so formed that
the end portions of the respective electrodes 6 and 7 overlap each
other at the boundary between the first electrode 6 and the second
electrode 7. With such construction, the electric field leaking
from the wiring 13 and switching element 14, which leaks from the
boundary between the first electrode 6 and the second electrode 7,
can more perfectly be shielded. Also, the tolerance of any pattern
deviation of the first electrode 6 and second electrode 7 at the
time of manufacture can be made larger.
[0074] In construction such that only one electrode (display
electrode) is formed on one substrate, it has been difficult to
suppress any display deterioration being caused by the electric
field leaking from wirings and switching elements at openings
between electrodes disposed in a matrix. However, in the
electrophoretic display device disclosed herein as the present
invention, the two electrodes first electrode and second electrode
are disposed in parallel to one substrate and these two electrode
faces are effectively used. Thus, it has become possible to
perfectly shield the electric field leaking from wirings and
switching elements at the boundaries between electrodes and
boundaries between pixels.
[0075] Now, of the first electrode 6 and second electrode 7
described above, any one electrode may be colored in the same color
as the charged electrophoretic particles 5 and the other electrode
may be colored in different color. For example;
[0076] in FIG. 1, the charged electrophoretic particles 5 may be
colored in black, the first electrode 6 in black, and the second
electrode 7 in white; or
[0077] in FIG. 9, the charged electrophoretic particles 5 may be
colored in black, the first electrode 6 in white, and the second
electrode 7 in black. Of course, the coloring is by no means
limited to these, and may freely be in any color combination. Also,
when color display is intended, the charged electrophoretic
particles 5 may be colored in black, one electrode of the first and
second electrodes in black, and the other electrode in red, green
or blue appropriately.
[0078] As methods of coloring the electrodes;
[0079] the electrodes themselves may be colored; or
[0080] colored layers shown by reference numerals 8a and 8b in FIG.
1 may be provided in addition to the electrodes. Either may be
employed. Here, the reference numeral 8a denotes a colored layer
which covers the first electrode 6, and the reference numeral 8b
denotes a colored layer which covers the second electrode 6. In an
example shown in FIG. 10, these colored layers 8a and 8b are both
so disposed as to be closer to the viewer's side than the both
electrodes, a first electrode 56 and a second electrode 57. of
course, their disposition is by no means limited to these. As shown
in FIG. 11, one colored layer 8a may be so disposed as to cover the
first electrode 56, and the other colored layer 8b to cover the
second electrode 57. Also, when the first electrode or the second
electrode is set transparent, the colored layers may be disposed
not on the viewer's side but on the opposite side. FIG. 12 shows an
example thereof, where the second electrode 57 is set transparent,
and its colored layer 8b is disposed beneath the second electrode
57. In place of a colored layer, a reflecting layer may be
disposed.
[0081] Here, in the case where the electrodes themselves are
colored as mentioned above;
[0082] the colors of electrode materials themselves may be
utilized; or
[0083] the colors of materials themselves for surface insulating
layers formed on the electrodes may be utilized.
[0084] An auxiliary electrode 10 to be set to the same potential as
the potential of the first electrode 6 may also be provided (FIGS.
15, 16, 17, 18 and 19) on an area including the position where the
absolute value of the horizontal component of electric field
vectors produced above the first electrode 6 assumes a minimum
value when a drive voltage of an equal potential different from the
potential of the first electrode 6 is applied to the respective
second electrodes 7 of adjoining pixels. The auxiliary electrode 10
may be an electrode disposed on the first electrode 6 via an
insulating layer, or the first electrode 6 has a protrusion
structure and the protrusion structure may be made to serve as the
auxiliary electrode 10 (FIG. 16). In either case, the auxiliary
electrode 10 may have an additional electrode structure on the
second substrate 1b side of the first substrate 1a at a place
conditioning as stated above (the area including the position where
the absolute value of the horizontal component of electric field
vectors produced above the first electrode 6 assumes a minimum
value when a drive voltage of an equal potential different from the
potential of the first electrode 6 is applied to the respective
second electrodes 7 of adjoining pixels). Providing the auxiliary
electrode 10 brings about the effect of improving the movement of
charged electrophoretic particles 5 in a region having a weak
electric field produced. Moreover, it brings about the effect of
lessening the influence of drive voltage of one pixel on any pixel
adjoining to that pixel. Especially when pixels adjoining to each
other differ in drive voltage, it brings about the effect of making
small any voltage variations at the position where the absolute
value of the horizontal component of electric field vectors
produced above the first electrode 6 assumes a minimum value when a
drive voltage of an equal potential different from the potential of
the first electrode 6 is applied to the respective second
electrodes 7 of adjoining pixels. This brings about the effect of
making the display quality level stable.
[0085] The insulating liquid 4 and the charged electrophoretic
particles 5 may also be encapsulated into a transparent film
microcapsule 11 and the resultant microcapsule 11 may be disposed
between the first substrate la and the second substrate 1b (FIG.
19). The use of such a microcapsule 11 makes it unnecessary to form
the partition wall 3. There are no particular limitations on the
size of the microcapsule 11. It may preferably be a certain measure
of uniform size large enough to cover each pixel region. Also,
construction making use of a microcapsule 11 having such a size
that it can cover a plurality of pixels is one of preferred
construction (FIG. 20).
[0086] As for the first substrate 1a and second substrate 1b,
usable are polymer films such as polyethylene terephthalate (PET)
film and polyether sulfone (PES) film and insulating materials such
as glass and quartz.
[0087] The electrodes 6, 7, 16, 17, 26, 27, 36, 37, 46, 47, 56 and
57 and the auxiliary electrode 10 may also be formed using any
materials as long as they are conductive materials capable of being
patterned.
[0088] An insulating layer 9 may further be so formed as to cover
the electrode 6 and so forth and the auxiliary electrode 10. In the
case where the insulating layer is formed, electric charges can be
prevented from being infected from the electrode 6 and so forth
into the charged electrophoretic particles 5. As materials used for
this insulating layer 9, preferred are materials causative of
formation of pinholes with difficulty and having a low dielectric
constant; stated specifically, amorphous fluorine resins, high
transparency polyimides, and PET. It may also preferably have a
film thickness of about 1 .mu.m or smaller.
[0089] As the insulating liquid 5, a colorless transparent liquid
such as silicone oil, toluene, xylene or high purity petroleum may
be used.
[0090] As the charged electrophoretic particles 5, a material
capable of showing good charge characteristics in the insulating
liquid may be used. For example, a resin such as polyethylene or
polystyrene may be used. When they are colored in black, carbon or
the like may be mixed in the resin. With regard to the particle
diameter of the charged electrophoretic particles, there are no
particular limitations. Usually, those having particle diameters of
from about 0.5 .mu.mm to about 10 .mu.m may be used.
[0091] As to the planar shape of pixels (the shape of pixels as
viewed from a viewer, in other words, the shape of each division
the partition walls 3 form), each pixel may have any shape as long
as the charged electrophoretic particles 5 can be prevented from
localizing (or moving across pixels). It is rectangular in the
examples shown in FIG. 2 and so forth, but may be hexagonal or any
other polygonal,
[0092] With regard to the first electrode, second electrode and
partition wall, their occupied area In one pixel may be in a ratio
of:
[0093] first electrode : second electrode : partition
wall=30:60:10
[0094] Typically stated, one pixel A is about 100 .mu.m.times.100
.mu.m in size, the charged electrophoretic particles 5 are 3 .mu.m
in particle diameter, and the space between substrates is about 50
.mu.m.
[0095] In the partition wall 3, a polymer resin may be used. As
methods of forming the partition wall 3, usable are:
[0096] a method in which a photosensitive resin layer is formed on
one substrate by coating followed by exposure and wet process
development;
[0097] a method in which partition walls are formed by printing;
and
[0098] a method in which partition walls are previously formed on
the surface of a light transmissive first is substrate by
molding.
[0099] As a material used for the microcapsule, it may include,
e.g., gelatin, polyvinyl acetate, ethyl cellulose, nitro cellulose,
polystyrene, polyethylene, polypropylene. epoxy resins, acrylic
resins, methacrylic resins, nylon, polyester, polycarbonate,
polyvinyl chloride, polyvinyl alcohol and sodium alginate. Also, as
methods for its formation, known methods such as phase separation
and polymerization may be used.
[0100] The present embodiments are effective as stated below.
[0101] According to the present embodiments, in respect of the two
pixels A adjoining to each other interposing the pixel boundary,
the first electrode 6 of one pixel and the first electrode 6 of the
other pixel are disposed at a position they are adjacent to each
other in the vicinity of the pixel boundary, and these first
electrodes 6 are so constructed as to be electrically connected to
have the same potential. Hence, the colored charged electrophoretic
particles 5 disposed in each pixel A are controlled only by the
voltage applied to the electrodes of that pixel A, without being
influenced by the voltage applied to the electrodes of the other
pixel A. As a result, any display disorder and decrease in contrast
can be made to less occur.
[0102] According to the present embodiments, the partition wall 3
is also provided, and hence the electrophoretic particles 5 can be
prevented from localizing (or moving from one pixel to the other
pixel), thus the display quality level is improved,
[0103] In the case where not the first electrodes 6 are formed
separately for each pixel but the first electrode 36 is integrally
formed for two pixels A as shown in FIG. 5 or 6, display devices
can be manufactured with ease.
[0104] In the case where three or more first electrodes and two or
more second electrodes are alternately disposed, the charged
electrophoretic particles 5 can be made to move in a short
distance, making it possible to form images at a high speed and
uniformly.
[0105] In the case where the insulating layer 9 is so formed as to
cover the electrode 6 and so forth, electric charges can be
prevented from being injected from the electrode 6 and so forth
into the charged electrophoretic particles 5.
[0106] In the case where the auxiliary electrode 10 is provided,
the influence of drive voltage of one pixel on any pixel adjoining
to that pixel A can be lessened to bring about an improvement in
display quality level.
[0107] In the case where the insulating liquid 4 and the charged
electrophoretic particles 5 are disposed in the state they are
encapsulated into the microcapsule 11, the charged electrophoretic
particles 5 can be prevented from localizing (or moving from one
pixel to the other pixel), thus the display quality level is
improved.
[0108] In the case where the wirings and switching elements are so
disposed as to be covered with the first electrode face or second
electrode face as viewed from the region in which the charged
electrophoretic particles are present, the influence on the driving
of charged electrophoretic particles, of any leaked electric field
caused by the wirings and switching elements can be lessened or
removed on account of the shielding effect attributable to the
first and second electrodes.
[0109] In the case where the first electrode 6 and the second
electrode 7 are formed on vertically shifted different planes so as
to have different heights from the substrate and also so formed
that the edge portions of the respective electrodes 6 and 7 overlap
each other at the boundary between the first electrode 6 and the
second electrode 7 (see FIG. 23A), the electric field leaking from
the wiring 13 and switching element 14, which leaks from the
boundary between the first electrode 6 and the second electrode 7,
can more perfectly be shielded. Also, the tolerance of any pattern
deviation of the first electrode 6 and second electrode 7 at the
time of manufacture can be made larger.
[0110] The present invention is described below in greater detail
by giving Examples.
Example 1
[0111] In this Example, the electrophoretic display device D.sub.1
having the structure shown in FIGS. 1 and 2 was produced.
[0112] In this device D.sub.1, each pixel A was formed in a size of
100 .mu.m.times.100 .mu.m, and the occupied area of the first
electrodes 6 (for the two), the occupied area of the second
electrode 7 and the occupied area of the partition wall 3 in each
pixel A were set in a ratio of 30(15.times.2):60:10.
[0113] When this electrophoretic display device D, was produced, an
aluminum thin film was formed on a PET film (200 .mu.m thick) as
the first substrate 1a, and was patterned by photolithography or
wet etching to form the first electrodes 6 and second electrode 7
in stripes and also to form wiring to connect the two first
electrodes 6. Then, a white colored layer 8b was so formed as to
cover these electrodes 6 and 7, and a black colored layer 8a was so
formed as to cover each first electrode 6. Here, the white colored
layer 8b was formed using an acrylic resin having a white pigment
such as alumina powder dispersed therein.
[0114] Next, an insulating layer 9 comprised of an acrylic resin
was so formed as to cover these colored layers 8a and 8b.
[0115] Thereafter, the surface of this insulating layer 9 was
coated with a photosensitive epoxy resin, followed by exposure and
wet process development to form partition walls 3. The partition
walls 3 were each 50 .mu.m in height.
[0116] At this stage, the second substrate 1b was not still bonded,
and hence a large number of depressions were formed by the first
substrate 1a and the partition walls 3. Then these depressions were
filled with silicone oil 4 as the insulating liquid and black
charged electrophoretic particles 5. Here, a mixture of polystyrene
with carbon was used to prepare the black charged electrophoretic
particles 5, having an average particle diameter of about 2 .mu.m.
The particles 5 showed positive charge polarity in the silicone
oil.
[0117] Next, a heat fusible adhesive layer pattern was formed on
the first substrate la at its areas to be bonded to the second
substrate 1b, and the second substrate 1b was placed on the
partition walls of the first substrate 1a under registration,
followed by application of heat to bond them together. A voltage
application circuit (not shown) was connected thereto to produce
the display device D.sub.1.
[0118] The electrophoretic display device D.sub.1 thus produced was
driven. Stated specifically, an applied voltage Vd1 to the first
electrode 6 was kept at 0 V, and an applied voltage Vd2 to the
second electrode at +50 or -50 V, where the voltage polarity was
reversed at intervals of 100 msec.
[0119] According to this Example, good black and white display was
obtained.
[0120] Also when black and white different display was performed in
adjoining pixels, any variations of contrast were not seen, making
sure that stable display contrast was obtainable.
Example 2
[0121] In this Example, the electrophoretic display device D.sub.1
having the structure shown in FIG. 5 was produced.
[0122] In this device D.sub.1 each pixel A was formed in a size of
100 .mu.m.times.100 .mu.m, and the occupied area of the first
electrodes 36, the occupied area of the second electrode 7 and the
occupied area of the partition wall 3 in each pixel A were set in a
ratio of 40:60:10.
[0123] When this electrophoretic display device D.sub.3 was
produced, an aluminum thin film was formed on a PET film (200 .mu.m
thick) as the first substrate 1a, and was patterned by
photolithography or dry etching to form the first electrodes 36,
second electrodes 7 and wirings B in the shapes shown in FIG. 6.
Then, a white colored layer 8b was so formed as to cover these
electrodes 36 and 7, and a black colored layer 8a was so formed as
to cover each first electrode 36. Here, the white colored layer 8b
was formed using an acrylic resin having a white pigment such as
alumina powder dispersed therein.
[0124] Next, an insulating layer 9 comprised of an acrylic resin
was so formed as to cover these colored layers 8a and 8b.
[0125] Thereafter, in the same manner as in Example 1, partition
walls 3 were formed, the depressions were filled with silicone oil
4 and black charged electrophoretic particles 5, and the second
substrate 1b was bonded.
[0126] Then, the electrophoretic display device was driven in the
same manner as in Example 1 As a result, the like effect was
obtained.
Example 3
[0127] In this Example, the electrophoretic display device D.sub.8
having the structure shown in FIG. 11 was produced. A plan view of
the device in this Example is also shown in FIG. 22.
[0128] In this device D.sub.8, each pixel A was formed in a size of
100 .mu.m.times.100 .mu.m, and the occupied area of the first
electrodes 56, the occupied area of the second electrode 57 and the
occupied area of the partition wall 3 in each pixel A were set in a
ratio of 30:70:10.
[0129] When this electrophoretic display device D.sub.8 was
produced, an aluminum thin film was formed on a PET film (200 .mu.m
thick) as the first substrate 1a, and was patterned by
photolithography or dry etching to form the rectangular first
electrodes 56, and second electrodes 57 in such a way that it
covered the whole display area other than the first electrodes. The
wiring 12 for connecting the first electrodes and the wirings 13
for connecting the second electrodes wore further formed; the
wirings 13 being each disposed at a position where the second
electrode is covered width the first electrode (see FIG. 22).
[0130] Then, in the same manner as in Example 1, the colored layers
8a and 8b, insulating layer 9 and partition walls 3 were formed,
the depressions were filled with silicone oil 4 and black charged
electrophoretic particles 5, and the second substrate 1b was
bonded.
[0131] The electrophoretic display device thus produced was driven
in the same manner as in Example 1.
[0132] According to this Example, good black-and-white display was
obtained.
[0133] Also when black and white different display was performed in
adjoining pixels, any variations of contrast were not seen, making
sure that stable display contrast was obtainable.
[0134] Moreover, any display deterioration due to the electric
field leaking from wirings and so forth was not seen at all.
Comparative Example
[0135] In this Comparative Example, the electrophoretic display
device shown in FIG. 13 was produced. A plan view of the device in
this Comparative Example is also shown in FIG. 21. The device
produced was driven in the same manner as in Example 1. As a
result, cases were seen in which the display was disordered in some
pixels because the electrophoretic particles 5 were influenced by
the drive voltage of adjoining pixels. Also when black and white
different display was performed in adjoining pixels, cases were
seen in which the display was disordered in some pixels because the
electrophoretic particles were influenced by the drive voltage of
adjoining pixels. Cases were also seen in which the display was
disordered in some pixels because the electrophoretic particles
were influenced by the electric field leaking from wirings (e.g.,
at the part of region A shown in FIG. 21).
[0136] As described above, according to the present invention, in
respect of the two pixels adjoining to each other interposing the
pixel boundary, the first electrode of one pixel and the first
electrode of the other pixel are disposed at a position they are
adjacent to each other in the vicinity of the pixel boundary, and
these first electrodes are so constructed as to be electrically
connected to have the same potential. Hence, the colored charged
electrophoretic particles disposed in each pixel A are controlled
only by the voltage applied to the electrodes of that pixel A,
without being influenced by the voltage applied to the electrodes
of the other pixel A. A a result, any display disorder and decrease
in contrast can be made to less occur.
[0137] According to the present invention, the partition wall is
also provided in the manner described previously, and hence the
electrophoretic particles can be prevented from localizing (or
moving from one pixel to the other pixel), thus the display quality
level is improved.
[0138] In the case where not the first electrodes are formed
separately for each pixel but the first electrode is integrally
formed in one body for two pixels, display devices can be
manufactured with ease
[0139] In the case where three or more first electrodes and two or
more second electrodes are alternately disposed, the charged
electrophoretic particles can be made to move in a short distance,
making it possible to form images at a high speed and uniformly
[0140] In the case where the insulating layer is so formed as to
cover the electrodes and so forth, electric charges can be
prevented from being injected from the electrodes into the charged
electrophoretic particles.
[0141] In the case where the wirings and switching elements are so
disposed as to be covered with the first electrode face or second
electrode. face as viewed from the region in which the charged
electrophoretic particles are present, the influence on the driving
of charged electrophoretic particles, of any leaked electric field
caused by the wirings and switching elements can be lessened or
removed on account of the shielding effect attributable to the
first and second electrodes.
[0142] In the case where the first electrode and the second
electrode are formed in different height on different planes and
also so formed that the end portions of the respective electrodes
overlap each other at the boundary between the first electrode and
the second electrode, the electric field leaking from the wiring
and switching element, which leaks from the boundary between the
first electrode and the second electrode, can more perfectly be
shielded. Also, the tolerance of any pattern deviation of the first
electrode and second electrode at the time of manufacture can be
made larger.
* * * * *